HV divider modificationsHV divider modifications

M. Raggi, T. Spadaro, P. Valente

&

G. Corradi, C. Paglia, D. Tagnani

MotivationsMotivations

Ringing & shoulder of the signal…

… and their effects on the time-over-threshold readout

Equivalent resistance Req= 3.36 M

At 1500 V maximum current is Imax=1500 V/ 3.36 M = 446 mA

Dissipated power:

PR= V·I = 107 V × 446 mA = 48 mW on R=240 kPR1= 2V·I = 214 V × 446 mA = 96 mW on R1=2RPtot=V·I = 446 mA × 1500 V = 670 mW total

V0=1500

Req=3.36M

Original dividerOriginal divider

V0=1500 V

Req=2.9M

Vclamp=280 V

Req= 2.9 M

Tension on divider is (1500 –Vclamp)Imax=(1500V-Vclamp)/ 2.9 M= 420 A

PR=VR × I = 100.8 V × 420 42.3 mW on each resistor (-6mW)Pdiodes= Vclamp × I = 280V × 420 = 117 mW ~ 60 mW per diode Ptot=Veq × I = 420 × 1500 V = 630 mW total

First dynode clamp Quenching of d10 d11 d12 and anodeQuenching capacitorsHV decoupling resistor (10 K)

Divider with 1st dynode clampDivider with 1st dynode clamp

• We use– R=240 K, V=voltage from HV supply

• For the totally resistive (original) divider Req=14 R

– G=iVi

=KNVN

– Vi=V/(14R)

• For the divider with diode clamp Req=12 R

– G=K1(V-V0) iVi

=K1(V-V0)KN-1V(N-1)

– Vi=(V-V0)/(12R)

Gain modelGain model

measurement measurement

Ratio between gain with resistive divider (old) and first dinode clamp divider (new)

K1 is already saturated, and thus cannot increase the gain. Increasing the tension on first dynode is useless.

Gain ratio can be improved by lowering the clamp voltage

(but only 10% better at 120 V)

Data/MC comparisonData/MC comparison

Final dividerFinal divider

Final dividerFinal divider

• 200 dividers already mounted

• only 1 with discharges (due to bad cable)

Gain comparisonGain comparison